Applicants claim priority under 35 U.S.C. xc2xa7119 of AUSTRIAN Application No. A 1301/98 filed Jul. 29, 1998. Applicants also claim priority under 35 U.S.C. xc2xa7120 of PCT/AT99/00188 filed on Jul. 27, 1999. The international application under PCT article 21 (2) was not published in English.
The invention relates to friction bearing having an intermediate layer with an aluminium base intended to enhance the mechanical properties of metallic substances of differing composition and a method of producing this friction bearing.
It is becoming more commonplace for multi-layered materials, in particular those used in plain bearings for components designed to rotate at high speeds, e.g. motor shafts, to be made such that the layered materials have a structure comprising basic shell bonding layer-bearing shell, especially if the bearing shell is made from a light metal alloy. The bonding layer fulfils an important function, particularly if the light metal alloy contains mechanically soft components such as tin, lead or similar, for example.
It is common practice to use a pure aluminium which is technically pure for the bonding layer, e.g. A 199.5. Over the course of development, light metal bearing alloys designed for use in modern motors and machinery have been required to withstand increasingly high loads and are fast becoming the weakest link of the multi-layered material. For example, pure aluminium has now been found to have distinct disadvantages as regards dynamic strength and heat resistance as compared with the new generation of light metal-bearing alloys.
Various concepts have already been suggested as a means of alleviating these problems. DE 40 37 746 Al and DE 43 12 537 Al, for example, propose using hardenable aluminium alloys for the bonding layer. However, since the production process used to join layers also involves several heat treatments, these hardenable materials rank on the highest level of strength in terms of their structure. In addition to a partially inadmissible adverse effect on the desired ductility, there is also the risk of over-ageing and hence an undesirable reduction in the service life of the finished product when the bearing point is subjected thermal and dynamic load.
A totally different approach is to use nickel, copper or similar layers, galvanised onto the base shell and dispense with an aluminium-based bonding layer altogether. Because of the low metallurgical affinity between bearing alloys of light metal on the one hand and nickel, copper or similar on the other, the bonding strength remains limited by the degree of adhesion and clamping, whereas if using pairs comprising a bonding layer of light metal/light metal bearing layer the adhesive joining forces produced in the bonding plane by means of heat treatment and diffusion improves the strength of an increased number of layers, which virtually exhibit the traits of metallurgical diffusion and reaction zones.
Various different aluminium alloys for friction bearings or friction bearings of differing compositions are known from WO 98/17833 A, WO97/22725 A, EP 0 672 840 A and DE 30 00 772 A. The different compositions of alloys described therein are intended to improve the durability of the soft phases, including those present in particularly high proportions, dispersed in the aluminium alloy. A number of ways of achieving this objective are described, for example by embedding hard particles as a means of interrupting an end-to-end tin network. EP 0 672 840 A in particular proposes a solution which involves using a hardenable aluminium alloy as an intermediate layer for friction bearings.
The underlying objective of the invention is to provide an intermediate layer with an aluminium base which will improve the quality of the bonding material, for example its mechanical properties, by matching the individual layers with one another more effectively.
This objective is achieved by a friction bearing having at least three layers of differing composition, at least one intermediate layer being made from an alloy with an aluminum base containing 0.015% by weight to 10% by weight of at least one element from the group consisting of So, Y, Hf, Ta, La, lanthanides and actinides and optionally a total of up to 12% by weight of at least one element from the group consisting of Li, Zn, Si, Mg or up to a total of 10% by weight of at least one element from the group consisting of Ma, Cu, Be, Ca, Zr, Mo, W, Ag or up to a total of 10% by weight of at least one element from the group consisting of Ti, V, Cr, Fe, Co, Ni or up to a total of 10% by weight of at least one element from the group consisting of Pd, Au, Pt, In, Ge, Sn, Pb, Sb, Bi, Te, and the remainder being formed by aluminum with smelt-related impurities. The advantage here is that an intermediate layer for a friction bearing made from an Al alloy can be provided, which does not exhibit any marked hardening behaviour whilst exhibiting a high ductility due to the finely dispersed distribution of A3M-phases and, in spite of the breakdown of solidified materials occurring during the manufacturing process due to heat treatments, high values of mechanical strength can be preserved. As a result, a product can be made which exhibits good thermal, static and dynamic stability. This intermediate layer is particularly well suited to plain bearings and the anti-friction layer of such plain bearings can be made from high-strength materials of a new kind. The advantage of this is the fact that this intermediate layer or the material used to produce it may have a high re-crystallisation temperature, which means that heat treatments or deformation processes can be performed at increased temperatures without giving rise to an undesirable reduction in hardness. Yet another advantage is that because of the possibility of using multiple combinations of individual elements, material characteristics can be freely adjusted within specific limits, thereby enabling the inherent cost of producing the intermediate layer to be controlled accordingly. On the other hand, however, being able to introduce radioactive elements or isotopes such as U235 into the alloy simultaneously means that tracers can be incorporated in the alloy for test purposes so as to monitor the behaviour of the material on different test machines.
By using different proportions of the large number of possible element combinations, particularly when using the intermediate layer as a bonding layer for a friction bearing, this layer can be readily adapted to specific requirements, in particular to the properties of the other layers comprising the friction bearing. The effects which can be achieved by introducing the specified elements into the alloy can be taken from the detailed description below.
Also different heat treatments provide an intermediate layer whose hardness is high enough to allow this intermediate layer to be combined with higher-strength materials such as new types of bearing materials, for example, and the process used to produce these intermediate layers can be shortened since it is possible to operate heat treatments at higher temperatures.
According to another aspect of the invention, a method is provided for producing a friction bearing, wherein the intermediate layer made from a previously hardened material made by a casting process, an extrusion process or a continuous casting process is rolled with at least one other material. As a result, the friction bearing can be made so that it has a surface which is suitable as a bearing for shafts rotating at high speed on the one hand, and, on the other hand, has a coating by means of which the forces transmitted onto the multi-layered material can be transferred. Advantageously, the quality of the bonding can be improved since the properties are intrinsic to multiple layers of the aluminum base.
The layers of the friction bearing may be rolled together and are tempered after every overall forming process by at least 25% and at most 91% in one or more forming step at a temperature in the range of between 85xc2x0 C. and 445xc2x0 C. This is of advantage because undesirable tension can be released after each massive forming process.
The friction bearing can be made by a whole range of possible methods, which means that the method best suited to the desired friction bearing can be selected. Thus, an anti-friction layer may be applied on top of the intermediate layer or the intermediate layer may be applied on top of the anti-friction layer and/or the intermediate layer may be applied on top of a base shell by a rolling process, a CVD process, galvanic processing, cathode sputtering, or a vacuum vapor deposition process.
The thickness of intermediate products of the friction bearing may be reduced by means of a plating process in a rolling mill in the range of 20% to 75% with each pass. Thus, the number of individual method steps can be selectively controlled during the plating process so that the manufacturing costs or time needed can also be controlled accordingly.
Advantageously, the friction bearing may be used as a thrust ring or thrust washer.